This invention relates to a process for the fluid lubrication drawing of composite metal wires and an apparatus used therefor.
Composite metal wires having a softer metal cladding around a harder metal core are well known in the art. Aluminum clad steel wires, for example, are widely used as overhead transmission and distribution lines or the like.
Such aluminum clad steel wires are of varying sizes, ranging from thin wires of about 2.0 mm in diameter to thicker wires. Thin wires have an aluminum cladding whose thickness decreases in proportion to the diameter. Thin wires are difficult to fabricate because thin wires, when fabricated by extrusion, for example, by extruding aluminum around a steel core, often suffer from such problems as reduced adhesion, nonuniform section, and aluminum cladding peeling. Sometimes the physical properties such as tensile strength of extruded wires do not fall in the appropriate range. In order to obviate these problems, attempts were made to draw aluminum clad wires for the reduction of their diameter.
The purpose of drawing is to produce a thin aluminum clad wire from the corresponding wire of a larger diameter. At the same time, improvements in yield and wire strength are achieved. Further, high speed drawing insures a satisfactory production speed.
However, aluminum clad wires could not be drawn by means of dies generally used for drawing single metal wires such as aluminum, copper or steel wires because a steel core having a substantial deformation resistance is coated with aluminum having a low deformation resistance.
Using a prior art die as shown in FIG. 1c, the inventors made an experiment of drawing an aluminum clad wire. It was found that aluminum accumulated at the entrance of the die and the wire was broken after it was drawn several ten meters. During this drawing, the steel core was not deformed at all and only the aluminum cladding was deformed. Excessive aluminum accumulated within the die, which acted like a wedge, causing wire breaking.
With this information the inventors speculated as follows. In drawing composite metal wires, drawing will be possible only when both a higher deformation resistant steel core and a lower deformation resistant aluminum cladding are deformed at the same reduction of area. In order to subject the steel wire to deformation, a forebody having a slightly larger diameter than a rod to be drawn and having a certain length is provided at the inlet of the die to restrain the aluminum accumulating at the die inlet, thereby increasing the pressure of aluminum between the inner wall of the die and the steel core. This increased pressure of aluminum causes the steel core to be deformed, enabling drawing. The inventors made various experiments to find that this speculation is correct. Based on these experiments, the inventors have completed the optimum process and apparatus for drawing composite metal wires.
Fleischmann et al, U.S. Pat. No. 3,080,962 (assigned to Copperweld Steel Company) discloses die drawing of aluminum clad steel wires. A set of three dies each having an approach angle of about 12.degree.-16.degree. is used to effect three-stage drawing of an aluminum clad steel wire while applying powder lubricant. This dry die drawing has some drawbacks. The die drawing devices with three dies built in are larger than usual devices. Powder lubricants such as metallic soap must be applied to draw wires. It is necessary from the point of view of product value and corrosion of wires to remove scales on the wire surface after drawing. In this respect, drawing processes using liquid lubricant are advantageous.